What is the difference between "scanf" and "scanf_s" in C ?

Question

scanf_s is recommended in VS-2017 after i used the regular scanf
https://code.sololearn.com/cx3Xheh5P2Gz/?ref=app

Answer 1

scanf_s() is a more secure version of scanf(). After the argument specifying the destination, the size of the destination must be provided. The program checks that the buffer is of the specified size before copying it to ensure that that there are no overwrites and malicious code isn't run.

Answer 2

Why doesn't it work on play ground ?